When surfing the web my computer will play a brief audio clip, why does it do that?

Sometimes will surfing the web and navigating from site to site, my computer will randomly play a brief 2-5 second (my guess) audio clip. The one I hear most often is "Your A Superstar". It sounds like Madonna singing the verse from her hit song Vogue.





This occurs at times randomly as well when the computer is idle. I understand some banner ads when I run my mouse over them they make noises, but this is not the case.





Any ideas what this is and more importantly how I can avoid it.|||they could be ads on the sides or pop ups


happens to me too|||well i get alot of pop ups that play audio, you know how you can still hear youtube if you minimize it, well popups like that come up minimized but you can still hear them, sometimes ill be looking at porn, then someone yells "FREE IPOD!!!"|||If you have AIM then it is probably the sound that one of your buddies has set for when they sign on and off.